September 1-7, 2023

Anomalous Warmth To Start Meteorological Fall

Meteorological Fall started September 1, but there was no hint of Fall in sight in the temperature department. The average temperature was above normal in every state in the Midwest during the first week of September (Figure 1). The range of temperature departures was anywhere from a whopping 8.1°F above normal in Minnesota to just 0.8°F above normal in Missouri. Right behind Minnesota was Wisconsin, with an average temperature of 7.5°F above normal for the period.

The average minimum temperatures were very above normal for the period in the Upper Midwest. Minimum temperatures were 5-10°F above normal for much of Minnesota, Wisconsin and Michigan (Figure 2). Minneapolis saw a daily minimum temperature of 75°F on September 3, which broke the record for highest daily minimum temperature record on that date.

The daily maximum temperatures were even more noteworthy. Almost 400 daily high maximum temperatures were broken, mostly in northern Iowa, Minnesota, Wisconsin and Michigan (Figure 3). For some locations, both the daily maximum and minimum temperatures were record-breaking. Most of the records occurred between September 2 and September 4, with the average maximum temperature for just those three days coming in at 95-100°F for many locations in Iowa, Minnesota and Wisconsin (Figure 4). The Twin Cities hit temperatures of 97°F and 98°F on September 3 and September 4, respectively. These were the first 95°F+ temperatures in September since 2012, and the first on consecutive days since 1978. Wausau, Wisconsin, and Eau Claire, Wisconsin both broke daily maximum temperature records on September 3 at 99°F and 100°F, respectively. Duluth, Minnesota recorded its first ever temperature at or above 95°F in September, with a temperature of 97°F on September 3.

Virtually No Precipitation Region-Wide

August ended dry and hot, and September started not much differently. Precipitation was hard to come by for the first week in September as most areas outside of the far northern Great Lakes saw less than 25 percent of normal rain (Figure 5). Much of drought-stricken Iowa, northern Missouri, and southern Minnesota saw no rain at all (Figure 6).

Heavy rains were concentrated in the Duluth, Minnesota area, as well as northwestern Michigan. A surface low came through northern Minnesota on September 5. As a result, areas in and around Duluth the recorded almost 4 inches of rain on September 5 alone. Video posted to social media confirmed flooded roadways in the wake of slow-moving storms in downtown Eveleth, Minnesota. As the same system very slowly moved east, parts of northwestern Michigan saw over 7 inches September 6-7.

Pesky and Persistent Drought

With little to no rain across most of the region, drought persisted and even expanded through out the last week. After a previous removal toward the end of August, abnormally dry (D0) conditions actually expanded back east into Indiana and western Ohio (Figure 7). Extreme drought (D4) was introduced to small areas of southwestern Wisconsin and southeastern Minnesota. Both severe drought (D3) and extreme drought (D4) were expanded in northern Minnesota, not far from Duluth. However, this was before recent heavy rains.

It’s important to note that two of the top five states for current drought coverage are in the Midwest. In Minnesota, 99.92 percent of land was classified as at least abnormally dry during the period, as well as 99.82 percent of land in Iowa, underscoring the severity of dry conditions across vast expanses of the Heartland.

Storm Reports

There were 74 storm reports for the period, most of which occurred on September 5 due to the previously mentioned surface low moving through the Upper Midwest. There were 16 hail reports, 4 of which were large hail of 2.0”+ diameter, as well as 54 wind reports, 7 of which were high wind reports of 65 mph+ (Figure 8). The National Weather Service in Duluth received several photos of large hail. One report, from Aitkin County, Minnesota, included a photo of egg-sized hail.

In terms of straight-line damaging winds, several noteworthy reports came out of St. Louis County, Minnesota. One 90 mph gust snapped or uprooted several 8-10 inch diameter pine trees near Skibo, Minnesota. A 94 mph gust caused a large evergreen tree with an estimated 14-18 inch diameter to fall onto a garage. A 107 mph gust gust snapped or uprooted several 12 inches + diameter trees near Aurora, Minnesota.